FR2616777A1 - NEW COMPOSITIONS COMPRISING CERAMIC MATERIALS - Google Patents

Abstract

The invention relates to novel compositions obtained by mixing ceramic materials, pseudoplastic polysaccharides and aqueous dispersions of film-forming polymer particles, and to the applications of the said compositions.

Description

- NEW COMPOSITIONS COMPRISING CERAMIC MATERIALS

  The present invention relates to new compositions obtained by mixing ceramic materials, pseudoplastic polysaccharides and aqueous dispersions of film-forming polymer particles, their uses, as applications, in substrate coating processes and in manufacturing processes. of sintered ceramic pieces, as well as the products

obtained by said processes.

  The compositions based on ceramic materials are used in many technical fields. We can thus cite their uses in processes for the preparation of ceramic pieces obtained by extrusion or by molding of said compositions, then

  by sintering the pieces thus comfortable in shape.

  However, the Applicant has been able to observe that the ceramic pieces obtained from the compositions described hitherto have poor mechanical properties, in particular as regards the

Tear resistant.

  In the processes for obtaining ceramic parts by molding, the compositions based on ceramic fillers are generally in the form of slips, that is to say compositions

  fluids consisting essentially of water and ceramic materials

  ques. These same types of slip used in the manufacturing processes

  molding, can also be used in coating processes

  tion and more particularly in enameling processes of

  ceramic or metallic parts.

  Thus, there is described in Canadian Patent No. 727,071 an aqueous suspension of xanthan gum, comprising in particular various

  ceramic materials, and which is used in enamelling.

  The Applicant has been able to observe that the compositions of this type had drawbacks both from the point of view of the elliptical slip and from the point of view of its application to

the mesh.

  Indeed, it has been observed that this type of slip lacked stability over time, which is reflected in particular by a

  increased viscosity of the slip.

  So when this type of slip is applied, for example

  by spraying, on the surfaces to be glazed, the spray rate

  sation is diminished, and we can even get a shutter

pistol nozzles.

  On the other hand, these slips, in order to provide sufficient enameling, must generally be applied in two successive layers, which does not however prevent the formation of an enameled surface having a "sheepskin" appearance. In addition, the enamel film obtained is fragile after drying, its appearance is powdery and makes handling in green raw delicate. In addition, the mechanical properties of the enamels thus produced are insufficient.

  especially as regards resistance to crushing.

  A first object of the invention is therefore a new composition which makes it possible to obtain ceramic parts having improved mechanical properties, particularly as regards

breaking strength.

  A second object of the present invention is a new aqueous fluid composition having improved stability over time. A third object of the invention is to obtain by using said aqueous fluid composition, coated and more particularly enameled surfaces, which can only be produced by the application of a single coating layer, not having

  of "sheepish" or powdery appearance, not being fragile after remsuya-

  and also having improved mechanical properties,

  especially with regard to resistance & crushing.

  To this end, the Applicant has developed a new composition characterized in that it is obtained by mixing at least

  at least one ceramic material, at least one pseudo- polysaccharide

  plastic and at least one aqueous dispersion of particles of

film-forming polymers.

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  Other characteristics and advantages of the invention appear

  will be clearer on reading the description which follows.

  As ceramic material suitable for the implementation of the present invention, any sinterable ceramic material can be used, either of the oxide type, for example silica, silicates such as mullite, cordierite, felspath; alumina; aluminates such as spinels, wallastonite; aluminosilicates such as clays; titanium oxide; titanates such as those of barium or magnesium; magnesia; zirconia; rare earth oxides such as thorium and cerium oxides; either of the non-oxide type such as, for example, boron carbide, silicon carbide or silicon nitride, or finally of the mixed type such as, for example, silicon and aluminum oxynitride (Sialon).

  Of course, this list of compounds is by no means limited to

  tive and is given only as an example.

  It is also possible to use mixtures of ceramic materials. The composition according to the invention also comprises at least

a pseudoplastic polysaccharide.

  As pseudoplastic polysaccharide, natural gum of plant or animal origin, modified natural gum or biogum can be used. These polysaccharides are

  generally used in powder or solution form.

  As natural gums, there may be mentioned alginates, guar gum, locust bean gum, Tara gum,

  cassia, Karaya gum, carrageenans.

  As modified natural gums which may fall within the scope of the present invention, there may be mentioned cellulose derivatives such as methylcellulose and my derivatives, hydroxypropylmethylcmllulose, carboxymethylcelluloma, ethylethylcelluloam, hydroxyethylcellulose, hydroxypropylcellulose, as well as , in general,

  other hydroxyalkylated derivatives of cellulose.

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  -Biogums are high molecular weight polysaccharides, generally over 1 million, obtained by fermentation

  of a carbohydrate under the action of a microorganism.

  As biogums which can be used in the composition which is the subject of the present invention, mention may be made of those

  obtained by fermentation under the action of bacteria or fungi

  gnons belonging to the genus Xanthomonas such as Xanthomonas begoniae, Xanthomonas campestris, Xanthomonas carotae, Xanthomonas hederae, Xanthomonas incanse, Xarnthomonas malvacearum, Xanthomonas papavericola, Xanthomonas phaseoli, Xanthomonas pisi, Xanthomonas

  vasculorum, Xanthomonas vesicatoria, Xanthomonas vitians, Xanthomo-

  nas pelargonii; to the genus Arthrobacter and more particularly the stabilizing Arthrobacter species, Arthrobacter viscosus; to the genus Erwinia; to the genus Azotobacter and more particularly the species Azotobacter indicus; to the genus Agrobacter and more particularly the species Agrobacterium radiobacter, Agrobacterium rhizogens,

  Agrobacter tumefaciens; alkaligens and more specific-

  the species Alcaligènes faecalis; in the genus Rhizobium; in the genus Sclerotium and more particularly the species Sclerotium rolfsii and Sclerotium glucanicum; to the genus Corticium; like

Sclerotinia; to the genus Stromatinia.

  As biogums which can be obtained by fermentation by the microorganisms described above, there may be mentioned gum

  xanthan, scleroglucan or succinoglycan.

  Among the aforementioned pseudoplastic polysaccharides,

  particularly preferred in the context of this invention

  xanthan gum, because of its interesting rheological properties and its high pseudoplasticity. Xanthan gum

  is commercially available in different industrial grades.

  The list of pseudoplastic polysaccharides mentioned above is given only by way of example. You can also use

  mixtures of pseudoplastic polysaccharides.

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  The aqueous dispersions of film-forming polymer particles which can be used in the composition according to the invention are also designated by the term "latex". They advantageously have a minimum film-forming temperature

  (TNFF) less than 50eC, and preferably less than 40C.

  They can in particular be latexes of vinyl or acrylic homopolymers or copolymers resulting from the polymerization of monomers generally containing 2 & 14 carbon atoms and

  one or two ethylenic bonds.

  Examples of polymers that may be mentioned are the copolymers of

  styrene and butadiene; homo or molecular weight copolymers

  the area of less than about 500,000, derivatives of acrylic and / or methacrylic monomers such as methyl, ethyl, propyl, butyl acrylates or methacrylates, and the copolymers derived from said acrylic or methacrylic monomers with styrene; homopolymers derived from vinyl esters of saturated aliphatic acids having up to 10 carbon atoms such as polyvinyl acetate, vinyl polypropionate and copolymers of such esters with lower C2-c4 olefins, with "versatate" of vinyl, with the acrylic or methacrylic monomers mentioned above or with the esters of maleic acid or fusaric acid preferably having 1 & 4

  carbon atoms in the alkyl radical.

  The concentration of polymer particles dispersed in the latex is generally between 30 and 65% by weight and preferably between 45 and 60% by weight relative to the total weight

said latex.

  The particle diameter is generally between 0.03

  and 5 microns and preferably between 0.05 and 1 micron.

  The pH of the aqueous dispersion of polymer particles is

  generally between 4 and 9.

6 1 6 7 7 7

  A latex which is very particularly preferred in the context of the present invention is an aqueous dispersion of particles of a copolymer derived from acrylic ester and styrene monomers, the concentration of which is 50% by weight of said latex, the pH equal to 8,

  the particle diameter being 0.1 micron and the TNFF 16 C.

  Such a latex is marketed by the company RHONE-POULENC

  under the name "Rhodopas DS 910".

  The compositions according to the present invention may also contain adjuvants, the nature of which will depend on the applications.

  subsequent of said composition and which are described below.

  The composition according to the invention can comprise from 0.01 to 2%, and preferably from 0.1 to 1%, by weight of pseudoplastic polysaccharides relative to the total weight of the composition as well as from 0.15 to 5% and preferably from 0.25 to 2% by weight of dry matter of the aqueous dispersion of polymer particles

  film-forming relative to the total weight of the composition.

  The composition according to the invention can be obtained for example by mixing the ceramic materials, the pseudoplastic polysaccharide and the aqueous dispersion of particles of film-forming polymers in a mill (for example a

ball) or in a mixer.

  In order to produce fluid compositions, water is added to the composition thus obtained. The amount of water required depends mainly on the nature of the ceramic materials and is such that the fluid composition has an adequate rheology, which can be determined by those skilled in the art according to the subsequent applications.

of said composition.

  The compositions according to the present invention can be used in processes for preparing sintered ceramic parts. These methods generally comprise the following stages - the composition according to the invention is shaped; - optionally drying the composition formed;

  - Then the dried composition is sintered.

  The shaping can be done in different ways depending on

  whether the composition is fluid or not.

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  Thus, when it is non-fluid, the composition can be shaped by extrusion. The composition is then introduced into an extrusion device in a pasty form obtained by adding an adequate amount of water. In this event it is possible to add to the composition according to the invention

  conventional extrusion additives (plasticizer, lubricant ...

  When it is fluid, the composition of the invention can

be shaped by molding.

  The introduction of the aqueous fluid composition into the mold

  can be done by injection or by casting.

  Conventional molding aids can then be

added to the fluid composition.

  -The ceramic pieces obtained by extrusion or molding are, once formed, most often dried at temperatures

between 20 and 150 C.

  Then they are sintered, that is to say they are cooked until

obtaining a dense product.

  The ceramic pieces obtained from the composition according to the invention, for example by means of a process as described

  above, have improved mechanical properties, in particular

  ment from the point of view of mechanical resistance to rupture.

  The aqueous fluid compositions according to the invention can also be used in surface coating processes and

  more particularly in enamelling processes.

  An enameling process according to the invention consists in obtaining

  tion of a substrate coated with a sintered ceramic material, produced according to the following steps: - said substrate is at least partially coated with an aqueous fluid composition according to the invention; - optionally drying the coated substrate;

- the coated substrate is sintered.

  The aqueous fluid compositions preferably used in the enamelling processes according to the invention are those which comprise, as ceramic materials, silica, silicates such as feldspar; aluminum minosilicates such as

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clays, wallastonite.

  Conventional glazing aids can be incorporated into the aqueous fluid composition according to the invention, such as fluxes such as chalk, talc, calcium carbonate, lead oxide, sodium oxide, oxide of potassium; opacifiers such as zinc oxide, tin oxide; dyes such as

  metal oxides such as copper oxide.

  Due to the presence in the composition according to the invention of pseudoplastic polysaccharides of natural origin or of biogum, it may be important to incorporate therein biocidal additives such as formaldehyde, pentachlorophenol derivatives such as CRYPTOGIL NA marketed by the RHONE-POULENC, or dichlorophene derivatives. The composition according to the invention can comprise from 0.005 to 0.2 and preferably from 0.01 to 0.1% by weight of biocides relative to the weight of the pseudoplastic polysaccharide present. The substrates preferably coated with the aqueous fluid composition according to the invention are of ceramic or metallic nature. The operation of coating the substrate with said composition is done by any known means and in particular by soaking, by

sprinkling or spraying.

  Spraying can be done using a spray gun

operating with compressed air.

  The coated substrate is then generally dried &

  temperatures between 20 and 150 C.

  Once dried, said coated substrate is sintered, that is to say

  that it is cooked until a dense product is obtained.

  The enameled supports thus obtained have very good mechanical properties, in particular as regards the resistance to rupture; the enamel does not have a "sheepskin" appearance and is not fragile after drying; its appearance is not powdery; easier handling of the mounted part; a single coating layer is sufficient although to obtain a greater thickness of enamel, it is entirely possible to apply one or more other layers of composition according to the invention on the

enamelled support.

  The following examples are given as an indication and cannot be considered as a limit of the domain and the spirit

of the invention.

  Examples 1 to 11 These examples were made from various compositions intended for enameling. Said compositions are obtained by mixing in a grinder of ceramic materials, xanthan gum and an aqueous dispersion of particles of

film-forming copolymers.

  These compositions according to the invention are designated by

capital letters.

  For comparison, compositions obtained by mixing the same ceramic materials and xanthan gum, but not containing an aqueous dispersion, were also produced.

  particles of film-forming copolymers.

  These compositions given for comparison are here designated

with lowercase letters.

  In this series of examples, the ceramic materials used are in the form of a formula I which comprises, in addition to the materials

  actual ceramics, glazing aids.

  Formula I includes Feldspar 40% Silica 20% Zinc Oxide 15% Chalk 10% Talc Frit 15% Colorant

  The percentages are expressed by weight.

  The xanthan gum used in these examples is

  RHODOPOL 23 marketed by RHONE-POULENC.

2 6 1 6 7 7 7

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  The aqueous dispersion of copolymer particles is a "latex" RHODOPAS DS 910, sold by the company RHONE-POULENC. This latex has a dry extract of 50% by weight, a pH equal to 8, a minimum film-forming temperature of

   C and a particle diameter of 0.1 micron.

  In this series of examples, the compositions according to the invention or those given by way of comparison are intended for enamelling; this is why they are added with water to

form slips.

  The proportions of the constituents entering the different slip are given in Table I below

Table I

  : Barbotine:% Formula I t Rhodopol:% Rhodopas DS 910: water a 65 0.1 0 34.9

A 65 0.1 1 33.9

b: 65: 0.2 0 34.8

B 65 0.2 1 33.8

c 65 0.3 0 34.7

C: 65: 0.3 1.5: 33.2

d: 65: 0.4 0: 34.6:

D 65: 0.4: 1: 33.6

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  il The percentages are given by weight relative to the weight

total of the composition.

  Examples 1 and 2 In these examples, the stability of the slip was tested at

over time.

  To do this, the viscosity of these slips was measured using a Rhéomat 30 de Contraves & Couette system, on the seventh

  then on the twentieth day after the formation of said slip.

  The results obtained are shown in Table II below

Table II

  : Examples: Slips: Viscosity in mPa.s: Variation of: ::: (at 0.9 s 1) viscosity:: --------------------- -------- in time:: * :: on the 7th day: on the 20th day:

: -: -_________ __ .:

1 c 9,300 4,560 51%

: 2 C 7 260 6 700 7%

  These examples clearly show that the slips comprising a polysaccharide and a latex conform to the invention exhibit a variation of vicosity over time, and therefore a stability,

markedly improved.

Examples 3 & 6

  In these examples, we tested the mechanical properties, and more particularly the mechanical resistance to crushing of enamel wafers obtained from slips, the compositions of which are described in Table I. Said enamel wafers were produced by slip filtration under a

  pressure of 5 bar, & through filter paper.

  Firmed enamel patties 90 mm in diameter and 6 to 8 min are obtained. They are then steamed at 50 C for

  48 hours, then & 110 C for two hours.

  The measurement of mechanical resistance & crushing is

  produced using an INSTRON press.

  The results obtained are shown in Table III below.

Table III

  Example: Barbotine: Mechanical resistance to crushing: starting point: (in kgf / cm2):

:. ....: ...... ::

3 b il: 3: b: - !:

4 B 24

c 13.3

6 C 32.7

  EXAMPLES 7 AND 8 In these examples, the flow rate of spray guns was reduced, the coapoaitions of which are described in table I. The gun spraying was carried out using a VGA 5027 gun,

the air pressure is 4 bar.

  The results obtained are shown in Table IV.

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Table IV

  : Example: Barbotine Spraying rate (in 1 / minute):.:: 7: b 2.26:

: - :: _:

8 B 3.5

  Examples 9 and 10 In these examples, the drying time was measured, which is the time necessary for the evaporation of the surface layer.

of water after enamelling.

  In these examples, the enameling was carried out by coating porcelain pieces by means of slips, the composition of which is described in Table I. The results obtained appear in Table V.

Table V

  : Example: Barbotine: Tepn of drying: of departure: (on seconds)

  ------------ - - - - - - - - - - - -

  mm m. m m m m mm m m m m m m. : 9: b: 30 s: 10 B: 25

  : - - - - - - -: - - - - - -: - - - - - - -: - -

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Example 11

  In this example, enamels were produced by coating pieces of porcelain with slurries, the compositions of which are described in Table I. It was found that the enamels obtained from slurries b and c have a "sheep-like" appearance and a powdery enamel to the touch after drying, while the enamels obtained from slip B and

  C do not have these drawbacks.

  Examples 12 to 15 Slips are produced containing xanthan gum and different proportions of Rhodopas DS 910 latex (which are identical to those used in the previous examples), as well as the following formula II: - Barium titanate 98.5 g - Darvant 7 1.5 g

  Barium titanate represents ceramic material.

  Darvant 7 is a dispersing polyelectrolyte, & 25% in

  aqueous solution and which is marketed by the company R.T.

  Vanderbilt. Said slips are then cast in plaster molds, then they are dried for 12 hours at temperature.

  ambient and for 2 hours at 120 C.

  Discs 23 mm in diameter and 4 mm thick are obtained. Resistance to rupture tests of these raw discs have

  were performed using a Zwick dynamometer.

  The results are collated in the following Table VI

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Table VI

  : Example: Composition of the starting slip: Resistance to: ------------------------------------ --- rupture (MPa)

::%:%:%:

  :: Gum: Latex: Formula: Water:: Xanthan: Rhodopas: - A

:: DS 910:

  _: .........__.........: _ ---- -------: -

12 0.6: 0 62 37.4 2.46

13 0.6: 1,622 36.5: 3.92

14 0.6 1.5 62 35.9 5.12

: 0.6 2: 62 34.5 4.90

  Examples 12 to 15 clearly show that the ceramic parts obtained from slip slip conform to the definition of the invention, have a resistance to breakage.

improved -

  Examples 16 & 19 The procedure is analogous to Examples 12 to 15. The concentration in xanthan gum is 1.2% and the resistance tests were carried out on raw pieces and on parts.

sintered & I 350 C.

  The results are collated in Table VII below.

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Table VII

  : Example: Composition of the slip: Resistance to rupture: :: starting point: (in MPa):

::::%% ::

  ::%: t:%:% ::: :: Rubber: Latex: Formula: Water: raw part: cooked part: :: Xanthan: Rhodopas: A ::::

:::: DS 910 :: :::

  :. ...: .....:. . ..: ....: ...:. .....: ......:

*: 16: 1.2: 0: 62: 36.8: 3.91: 39.8:

: 17: 1.2: 1: 62: 35.8: 6.55: 43.8:

  : 18: 1.2: 1.5: 62: 35.3: 6.87: 46.9:

: 19: 1.2: 2: 62: 34.8: 9.08: 44.1:

  : - - - - - - - - -: - - - - - - - - -: - - - - - - - -: - - - -

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Claims (30)

  1. Composition characterized in that it is obtained by mixing at least one ceramic material, at least one pseudoplastic polysaccharide and at least one dispersion   aqueous of film-forming polymer particles.   2. Composition according to claim 1 characterized in that   that said composition is dispersed in water.   3. Composition according to one of claims 1 or 2   characterized in that the aqueous dispersion of film-forming polymer particles has a minimum temperature   film formation less than 50 C.   4. Composition according to one of claims 1 to 3   characterized in that the aqueous dispersion of film-forming polymer particles has a minimum temperature   lower film formation & 40 C.   5. Composition according to one of claims 1 to 4   characterized in that the above-mentioned aqueous dispersion of film-forming polymer particles is an aqueous dispersion of a vinyl and / or acrylic homopolymer or copolymer resulting from the polymerization of monomers comprising from 2 to 14 carbon atoms and 1 or 2 ethylenic bonds.   6. Composition according to one of the preceding claims   characterized in that said aqueous dispersion of film-forming polymer particles is an aqueous dispersion of styrene and butadiene copolymers; homocopolymers or copolymers of molecular weight less than 5M 000, derived from acrylic and / or methacrylic monomers; copolymers derived from said monoeres   acrylic or methacrylic with styrene; dhcmo-   poleymers derived from vinyl esters of saturated aliphatic aids having up to 10 carbon atoms and copolymers of said esters with lower C2-C4 olefins, with vinyl versatate, with precitis acrylic or methacrylic monomers or with esters of maleic acid or fumaric acid preferably having from 1 to 4 carbon atoms in the alkyl radical.   7. Composition according to one of the preceding claims   characterized in that the concentration of polymer particles in the above-mentioned aqueous dispersion is between 30 and 65% by weight relative to the total weight of said aqueous dispersion.   8. Composition according to one of the preceding claims   characterized in that the particle diameter of said aqueous dispersion is between 0.03 and 5 microns.   9. Composition according to one of the preceding claims   characterized in that said composition comprises from 0.15 to 5% by weight of dry matter of the aqueous dispersion of particles of film-forming polymers relative to the weight total of said composition.   10. Composition according to claim 9 characterized in that said composition comprises from 0.25 to 2% by weight of dry matter of the aqueous dispersion of particles of film-forming polymers relative to the total weight of the composition.   11. Composition according to one of the preceding claims   characterized in that the pseudoplastic polysaccharides are gums of plant or animal origin, modified natural gums or biogums obtained by   carbohydrate fermentation by microorganisms.   12. Composition according to claim 11 characterized in that said biogums are obtained by fermntation of carbohydrate by bacteria or chupignon belonging to the genera Xanthomonas, Arthrobacter, Azotobacter, Agrobacter, Alkaligènes, Erwinia, Rhizobium,   Corticium, Sclerotinia, Stromatinia or Sclerotium. 26 16777   13. Composition according to one of claims 11 or 12   characterized in that the biogums are gum   xanthan, scleroglucan or succinoglycan.   14. Composition according to one of the preceding claims   characterized in that said composition comprises from 0.01 to 2% by weight of psaeudoplastic polysaccharides per   relative to the total weight of the composition.   15. Composition according to claim 14 characterized in that said composition comprises from 0.1 to 1% by weight of pseudoplastic polysaccharides relative to the weight total of the composition.   16. Composition according to one of the preceding claims   characterized in that the ceramic materials are sinterable ceramic materials.   17. Composition according to claim 1 characterized in that the sinterable ceramic materials are chosen from   metal oxides and / or silicon oxides.   18. Method for obtaining a substrate coated with a sintered ceramic material of the type comprising the following steps a) at least partially coating said substrate with a composition based on ceramic materials, b) optionally drying the substrate coated, c) the coated substrate is sintered, said method being characterized in that the above composition is a   composition according to one of claims 1 to 17.   19. The method of claim 18 characterized in that the   substrate is ceramic or metallic in nature.   20. Method according to one of claims 18 or 19   characterized in that the drying operation is carried out   at dem temperatures between 20 and 150C.   21. Melon process one of claims 18 to 20 characterized   in that the sintering operation is carried out at a   temperature allowing obtaining a dense product.   22. Method according to any one of claims 18 & 21   characterized in that the operation of at least partial coating of the substrate is done by soaking, sprinkling or spraying.   23. Method according to one of claims 18 to 22 characterized   in that the ceramic materials of the composition according to   one of claims 1 to 17 are silica,   silicates and / or aluminosilicates.   24. Method according to one of claims 18 to 23 characterized   in that the composition according to one of claims 1   to 17 includes conventional glazing additives.   25. Process for manufacturing a sintered ceramic part of the type comprising the following steps: a) a composition based on ceramic materials is formed, b) the composition formed is optionally dried, c) the composition formed is sintered, said composition process being characterized in that the above composition is a   composition according to one of claims 1 to 17.   26. Method according to claim 25 characterized in that   said ceramic piece is easy to shape by molding.   27. The method of claim 26 characterized in that said ceramic part is shaped by molding   produced by injection or by pouring the composition.   28. The method of claim 25 characterized in that said sintered ceramic part is molded by extrusion.   29. Method according to one of claims 25 to 28 characterized   in that the drying temperature is reduced to 20 and 150 C.   30. Method according to one of claims 25 to 29 caractériL   in that the sintering operation is carried out at a   temperature allowing obtaining a dense product.